THE  SEPARATION  OF  COLUMB1UM 
AND  TANTALUM 


BY 

SAMUEL  BENJAMIN  LIEB 


THESIS 


FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIE 

IN 

CHEMICAL  ENGINEERING 


COLLEGE  OP’  LIBERAL  ARTS  AND  SCIENCE 


UNIVERSITY  OF  ILLINOIS 


1 922 


N G E 


UNIVERSITY  OF  ILLINOIS 


V > 0 ^ 


SI 


kSJC  _2_S 192.2 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 

Saisu.el.J3K  11  j amin-.Li.gfr 

entitled 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
degree  OF B_a c h e_l or _ of  _ _S c jl e 11c e _ in_ _Ch e_ini_c al _ Engine e ri  ng 


LVL 


Instructor  in  Charge 


Approved  : 


HEAD  OF  DEPARTMENT  OF 


500175 


' 


Acknowledgment 


To  Dr. 

kindly  criticism  and 
pleasure,  the  author 


B.S.  Hopkins,  under  whose  supervision, 
instructive  advice  this  work  became  a 
wishes  to  extend  his  utmost  apprecia- 


t ion. 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/separationofcoluOOIieb 


The  Separation  of  Columbium  and  Tantalum 


Table  of  Contents 


Introduction  

Theory  of  Double  Fluoride  Process  . . . 

The  Double  Fluoride  Process  

Experimental  

Photographs  of  Crystals  

Conclusion  

Theory  of  Selenium,  Oxychloride  Hethod 
The  Selenium  Oxychloride  Process  . . . . 
Preparation  of  Selenium  Oxychloride  . 

Experimental  

Conclusion  

Bibliography  


Page 

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3 

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4 
6 

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8 
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11 

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14 


1 


The  Separat ion  of  Columbium  and  Tantalum 


For  a great  many  years,  in  fact  ever  since  the  discovery 
of  the  elements  about  a century  ago,  chemists  have  been  per- 
plexed by  the  problem  of  the  separation  of  columbium  and 
tantalum.  The  resemblance  of  the  elements  and  their  cor- 
responding compounds  in  both  physical  and  chemical  proper- 
ties is  so  strong,  that  no  point  of  divergence  can  be  found, 
sharp  enough  to  base  a means  of  separation  upon  it. 

A number  of  methods  for  a solution  of  this  problem  have 

2.;3 

been  proposed,  but  the  one  found  to  be  best  applicable  was 


that  of  Marignac. 


. 


. 


' 


2. 


* 

The  Theory  of  the  Double  Fluoride  Process 

S",6. 

Marignao  suggested,  crystallization  of  the  normal  potassium 
f luotantalat e,  E2Ta  Fr  , under  such  conditions  of  acidity  and 
concentration  of  potassium  fluoride,  that  the  columbium  should 
form  the  soluble  oxyfluoride,  KpbO^.Hp.  The  separation  is 
based  on  the  fact  that  the  two  double  fluorides  are  not  iso- 
morphous,  and  therefore  no  mixed  crystals  should  be  formed. 

Obviously,  this  theory  was  accepted  as  a tentative  solu- 
tion of  the  difficulty.  The  experimental  details  of  the 
problem  were  then  studied,  and  the  following  method  was 
adopted. 


■ - 


* 


- 


3. 


The  Double  Fluoride  Process 

i 

The  method  here  given  is  that  of  Wolcott  Gibbs,  and 
is  very  similar  to  the  Marignac  process,  having  preceded  the 
latter . 

The  finely  pulverized  mineral  is  fused  with  3 times  its 
weight  of  potassium  fluoride.  This  fusion  is  then  digested  with 
boiling  water  which  has  been  acidified  with  hydrofluoric  acid. 

Now  the  solution  is  filtered  to  remove  quart z, potassium . fluosili- 
cate  and  calcium  fluoride. 

The  next  step  is  precipitation  of  any  tin,  tungsten  or 
molybdenum  present,  by  means  of  hydrogen  sulphide.  Then 
evaporate  to  dryness,  add  enough  sulphuric  acid  to  expel  all 
the  fluoride  present.  Then  boil  with  a large  amount  of  water, 
and  the  needles  of  the  tantalum  compound  will  be  precipitated. 
These  are  filtered  off,  and  upon  standing,  or  further  concen- 
tration, the  thin  transparent  plates  of  the  columbium  salt  ap- 
pear . 


. 


. 


■ 


I 

. 

♦ 

« 


4. 


Experiment  0/1 

The  residues  of  Norwegian  Fergusonite,  which  had 
been  previously  treated  to  remove  the  rare  earth  content,  were 
used  as  the  source  of  columbium  and  tantalum.  The  mass  was 
dried  and  finely  pulverized.  Then  25  grams  of  it  was  intimate- 
ly mixed  with  75  grams  of  well  ground  potassium  fluoride. 

To  this  mixture  in  a platinum;  crucible,  some  hydroflu- 
oric acid  was  added,  and  the  pasty  mass  evolved  heat  immedia- 
tely. It  was  allowed  to  stand  for  a day,  acid  being  added  with 
vigorous  stirring  when  the  mass  became  hard.  After  removal 

of  excess  acid  on  the  water  bath,  the  material  was  dried,  and 

o 

then  heated  to  fusion  at  800  C.. 

The  fused  mass  was  of  a whitish  yellow  color,  but 
repulverization  and  fusion  gave  an  almost  pure  white  mass.  The 
melt  was  then  digested  by  boiling  with  water  and  hydrof luoric 
acid,  and  filtered  to  remove  impurities.  The  hot  filtrate  was 
allowed  to  stand  in  a rubber  dish,  and  upon  cooling,  a cu/riad 
of  glistening,  white,  laminated  crystals  settled  to  the  bottom. 
These  were  filtered  off,  and  hydrogen  sulphide  was  passed  into 
the  solution.  A brown  precipitate  settled  out  and  this  was 
filtered  off.  Confirmatory  tests  showed  it  to  be  molybdenum 
sulphide . 

Now  the  filtrate  was  neutralized  with  ammonia,  bring- 
ing down  the  remaining  impurities,  such  as  rare  earth,  iron,  etc. 
which  I removed.  The  filtrate  was  now  evaporated  to  dryness. 


. 


. 


* 


. 

. 

* i * 

. 


5 . 

sulphuric  acid  added  to  expel  the  fluorine  present,  and  then 
boiled  with  water.  Upon  concentration  of  the  solution  the 
tantalum  salt  appeared  in  needle-shaped  crystals,  and  upon 
further  concentration  the  transparent  plates  of  potassium 
columbium  oxyfluoride  were  precipitated. 

Necessary  weighings  were  made,  and  it  remained  to 
test  the  salts  qualitatively.  First  some  of  the  laminated 
salt  was  dissolved  in  water,  and  acidified  with  a drop  of  hydro- 
chloric acid.  To  this  solution,  one  of  tannic  acid  in  alcohol 
was  added,  and  a brick-red  color  resulted,  indicating  columbium. 

The  same  test  on  the  needle-like  salt  gave  a sulphur  yellow  color, 
indicating  tantalum. 

Then  again,  to  a water  solution  of  each  salt  I added 
an  excess  of  potassium  thiocyanate,  then  particles  of  zinc, 
followed  by  strong  hydrochloric  acid.  At  once  the  laminated 
salt  solution  turned  brown,  while  the  other  gave  no  color  reaction, 

As  a final  confirmatory  test,  I added  to  a solution 
of  each  salt  some  potassium  f errocyanide,  and  heated  to  boiling. 
The  solution  containing  the  laminated  crystals  produced  a green- 
ish blue .precipitate . This  reaction  confirmed  the  original  salt 
as  the  columbium  compound.  The  solution  of  the  needle-like  salt 
turned  yellow,  proving  the  presence  of  the  tantalum  salt. 

After  repeated  separations  of  various  samples,  I got 
an  average  composition  as  follows: 

K£bOFr  . Ha0  — 63.9$  & KaTaFr  — 3.2$ 


. 


* 


. 


- 


. 


- 

. • 


6. 

Photographs  of  Crystals 


Potassium  Fluoxycolumbate 


Magnif . 3 l/3  times 


Magnify  4 times 


Pot.  Fluoxycolumbate 
Magnif.  10  times 


Potassium  Fluotantalate 
Magnif.  10  times 


7. 

Conclusion 

Although  the  double  fluoride  method  is  a fair  one,  there 
are  a number  of  disadvantages  in  it.  First  of  all  the  ratio  of 
the  solubility  of  the  columbium  compound  to  that  of  the  tantalum 
is  only  about  10  to  1,  potassium  columbium  oxyfluoride  being  sol- 
uble in  13  parts  of  hot  water,  while  potassium  f luot antalate  re- 
quires 130  parts.  Therefore,  many  recrystallizations  are  ne- 
cessary, before  even  an  approximate  separation  may  be  attained. 

Neither  element  can  thus  be  obtained  absolutely  pure,  and 
the  limit  of  error  is  seen  to  be  at  least  10 $.  Furthermore,  ad- 
ditional error  may  be  introduced  thru  difficulty  in  maintaining 
the  proper  concentrations  of  hydrofluoric  acid  and  potassium 
fluoride.  If  the  acidity  is  too  great  the  columbium  forms  a 
normal  fluoride;  if  too  low,  the  tantalum  may  form  an  oxyfluo- 
ride; in  either  case  the  basis  of  separation  is  destroyed. 

If  too  much  or  too  little  potassium  fluoride  is  present, 
double  fluorides  are  formed,  in  which  the  ratio  of  potassium 
fluoride  to  columbium  or  tantalum  pentaf luor ide  is  more  or 
less  than  2:1.  Finally,  the  double  fluoride  method  is  extreme- 
ly laborious  and  consumes  a great  deal  of  time,  in  addition  to  re- 
quiring the  use  of  platinum  vessels. 


. 


* 

' 

. 

* 

•i 


. : 


8. 


Theory  of  the  Selenium  Oxychloride  Process . 

6. 

Lenher  discovered  that  columbium  oxide  is  soluble  in  a 
mixture  of  sulphuric  acid  and  selenium  oxychloride,  while  tanta 
lum  is  almost  insoluble  in  the  same  reagent.  Evidently  this 
ought  to  serve  as  a new  and  better  means  of  attacking  the  old, 
puzzling  problem.  Work  was  begun  along  this  theory,  and  the 
ideal  experimental  conditions  for  accomplishing  the  separation 
were  found  by  long  continued  research. 


. 


- 


9 . 

The  Selenium  Oxychloride  Method. 

The  mixture  of  colurnbium  and  tantalum  oxides  is  separated, 
together  with  titanium  when  present,  by  the  ordinary  methods  of 
procedure,  from  the  remaining  elements.  Then  the  percentage 
of  mixed  oxides  in  the  sample  is  determined.  Now  a weighed 
sample  of  the  ignited  oxides  is  boiled  with  50  cc . of  a 1:1  mix- 
ture of  selenium  oxychloride  and  sulphuric  acid  ( cone.)  in  an 
ehrlenmeyer  flask  on  a sand-bath  for  half  an  hour.  The  boil- 
ing must  not  be  so  vigorous  as  to  give  off  clouds  of  vapor. 

The  contents  of  the  flask  are  then  allowed  to  cool,  and 
then  decanted  with  suction  thru  a weighed  Gooch  crucible.  In 
this  decantation,  solid  particles  should  not  be  allowed  to  en- 
ter the  filter,  because  they  would  thus  escape  the  necessary 
subsequent  extraction. 

The  filtrate  is  poured  into  a large  volume  of  water,  and 
the  resulting  solution  is  heated  to  boiling.  A voluminous 
white  precipitate  of  hydrated  colurnbium  pentoxide  indicates  the 
presence  of  colurnbium  in  the  mixture.  The  residue  left  in  the 
flask  after  decantation  is  boiled  with  20  cc.  of  the  reagent  for 
15  minutes.  The  solution  is  then  decanted  thru  the  Gooch  cru- 
cible, and  the  filtrate  poured  into  water.  This  repeated  extrac 
tion  is  continued  until  hydrolysis  of  the  filtrate  gives  only  a 
faint  white  precipitate  due  to  traces  of  dissolved  tantalum  pen- 
toxide . 


' 


10. 


By  the  above  method  of  procedure,  the  stages  of  solution 
of  the  columbium  oxide  can  be  ascertained,  and  the  number  of 
extractions  thus  determined  in  order  to  effect  complete  removal 
The  next  step  in  the  process  is  to  transfer  the  undissolved 
tantalum  pentoxide  to  the  crucible,  by  means  of  jet  from  a wash 
bottle.  It  is  not  necessary  to  wash  the  oxide  completely , since 
all  the  decomposition  products  of  the  reagent  are  volatile. 

The  crucible  is  now  ignited  and  weighed,  and  the  in- 
crease in  weight  represents  the  amount  of  tantalum,  pentoxide 
in  the  sample.  The  quantity  of  columbium  plus  titanium  is 
determined  by  the  difference  in  weights.  Titanium  is  best 
determined  color imetrically  in  a separate  sample,  and  its 

weight  is  deducted  from  that  of  its  mixture  with  columbium. 

9. 

Henry  Baldwin  Merrill  applied  this  method  to  synthetic 
mixtures  of  columbium  and  tantalum  pentoxides,  and  found  the 
maximum  error  to  be  about  3 per  cent.  Thus,  the  process  is 
seen  to  be  not  only  more  rapid  and  simple  in  operation  than 
the  Marignac  process,  but  more  accurate  to  the  extent  of  7 per 


cent . 


* 


* 


. 

' 


- 

. 


* 


m . 

Preparation  of  Selenium  Oxychloride 

7. 

Following  the  method  used  by  Lenher,  the  preparation  of 
selenium  oxychloride  was  attempted  by  the  interaction  of  selen- 
ium dioxide  and  tetrachloride.  The  addition  of  boiling  nitric 
acid  to  powdered  selenium,  succeeded  by  the  heat  decomposition 
of  the  selenious  acid  formed,  yielded  a pure  white  product  of 
selenium  dioxide. 

However,  the  preparation  of  selenium  tetrachloride  as 

ip 

advised  was  not  very  successful.  Vanino  gives  a good  method 
in  which  the  elements  selenium  and  chlorine  are  mixed  in  the 
dry.  The  apparatus  used  is  shown  in  the  diagram. 


The  reaction  took  place  violently  with  the  generation 
of  much  heat,  and  the  tetrachloride  distilled  over  into  the 
long  tube. 

The  dioxide  and  tetrachloride  were  then  mixed  and  dry 
distilled  under  reduced  pressure.  The  product  obtained  was 
very  much  contaminated  with  red  colloidal  selenium.  Repeated 
vacuum  distillation  did  not  purify  the  compound.  Furthermore, 
extraction  of  the  impurity  with  carbon  disulphide  was  found  to 
be  impractical.  The  pure  selenium  oxychloride  was  therefore 
bought  and  thus  used. 


12  . 

Experimental 

Some  potassium  fluoxycolumbate  crystals,  obtained  by  the 
double  fluoride  process,  were  ignited  to  the  pentoxide.  With 
this  compound  as  a basis,  the  selenium  oxychloride  method  was 
applied  in  an  attempt  to  determine  increased  efficiency  of  the 
latter  process,  as  described  above. 

However,  none  of  the  tantalum  salt  was  obtained  thru 
this  means . . 

Next  a quantity  of  the  Fergusonite  residues  was  fused  with 

10 

9 times  its  weight  of  potassium  bisulphate.'  This  fusion  was 
digested  with  water,  the  insoluble  part  containing  columbium 
and  tantalum,  and  as  impurities,  tin,  titanium,  silica  and 
possibly  tungsten.  The  latter  were  removed  by  heating  with 
yellow  ammoniumi  sulphide,  and  then  treating  with  dilute  sulphur- 
ic acid  to  dissolve  out  the  iron  sulphide. 

How  the  oxides  were  washed  with  boiling  water  and  dried. 

tt. 

After  ignition,  the  color  of  the  oxides  was  almost  pure  white. 

The  selenium  Oxychloride  was  then  used  as  a means  of  separation 
of  the  columbium  and  tantalum  oxides,  as  described  above. 

By  this  method  I found  the  contents  to  be: 

Cb2  Ojj-  — 45.5 fo  and  Ta40tf—  33.3 <?0 


m 


• • ■ ; 


. 

■ 


♦ 


* 


. 


. 


13. 

Conclusion . 

The  selenium  oxychloride  process  is  very  effective  when 
used  in  conjunction  with  the  opening  up  of  an  ore  by  a fusion 
in  order  to  obtain  a mixture  of  the  tantalum  and  columbium 
oxides.  The  bisulphate  fusion  is  preferable  in  this  connection, 
to  that  of  the  bifluoride. 

Furthermore,  the  oxychloride  is  much  more  rapid  than 
the  double  fluoride  process,  since  in  the  former  the  analyst 
is  not  forced  to  lose  time  in  waiting  for  complete  crystal- 
lizations to  take  place,  as  in  the  latter. 

In  short,  it  is  likely  that  the  selenium  oxychloride  may 
replace  the  old,  reiied-upon  double  fluoride  process,  in  the 
near  future,  notwithstanding  that  the  applicability  of  the 
former  method  is  rather  limited. 


' 


■ 


■ 


. 


14 


Bibliography 


Vol . 


1.  Am.  Journal  Sci.  & Arts  Ser.  II  3_7 

2.  Chem.  Abstracts  3 

3 . " News  98 

4.  Journ.  f.  Prakt . Chemie  94 

5 . " « " " 97 

6 . ” » » n 102 


7.  Journal  Am.  Chem.  Soc _42 

8 . « " » ,f  43 

S . " « . »«  » 43 

10 . " " " « 27 

11.  " " " n 30 

12,  Praparative  Chemie  By  Vanino  1 


Page 

357 

758 

1 & 243 

304 

449 

448 

2498 

28 

2378 

1368 

1637 

97 


